The present invention relates to a klystron unit and, more particularly, to an improvement in a multicavity klystron unit.
In a klystron unit as known, an electron gun which generates an electron beam and a collector section for collecting the electron beam are arranged oppositely to each other on a common axis. An input resonance cavity, one or more intermediate resonance cavities and an output cavity are located along a beam path between the gun and the collector section. Drift tubes for defining the beam path which the beam passes are provided between these cavities, and a tube assembly is formed of these drift tubes and the resonators. This assembly is placed in an electromagnet coil assembly and the beam is focused by a magnetic field produced by the coil assembly.
When a signal of a continuous wave or a low modulation frequency is amplitude-modulated in such a multicavity klystron unit, the klystron is operated in a sufficiently stable and high input-to-output conversion efficiency. When the klystron, however, amplifies a pulse signal or a pulsating signal such as a synchronizing signal of a television broadcasting radio wave, an output signal is frequently vibrated at the frequency around several MHz as shown by reference characters A1 and A2 in FIG. 1, or the output level is unstably varied as shown by reference characters B1 and B2 in FIG. 2. It is confirmed that this phenomenon occurs intermittently at a level higher than the output level of approx. 60% of the saturated output. When the standing wave ratio of an input signal is deteriorated, such a phenomenon occurs even at the output level less than 50% of the saturated output. In order to prevent the occurrence of this undesirable phenomenon, it is necessary to operate the klystron in the state that the input-to-output conversion efficiency is reduced to less than 50%. A method of detuning the tuning frequency of an intermediate cavity disposed in the nearest position to the output cavity to sufficiently high frequency sufficiently higher than the operating frequency and thereby reducing the velocity distribution of an electron beam which flows into the gap of the output cavity is disclosed as one method of preventing such a phenomenon in Japanese Patent Laid-Open No. 149,471/1977. According to this method, the reverse flow of the electrons from the vicinity of the output cavity toward the gun can be suppressed, thereby obtaining a klystron which can provide approx. 55% of input-to-output conversion efficiency.
This is one remedy to improve the above drawback, but since the intermediate cavity which is disposed at the nearest position to the output cavity is designed to be detuned to a frequency much higher than the tuning frequency which can originally provide the maximum efficiency, the efficiency is not yet sufficiently improved and this klystron is further required to be improved.